In the continued push for cleaner technology, a concurrent growth trend is the better mining and utilization of mineral resources. As used herein, mining of mineral resources includes not only the extraction from the ground, but also the processing of the resource to extract in its raw or otherwise usable form. The mining of mineral resources follows a complicated process that includes the generation of slurries concentrates having mineral slurries having high moisture content. The slurry contains the important minerals, but needs to be properly separated from the moisture content.
Concentrated mineral slurries have been the subject of dewatering processes for many years. The production includes mineral concentration facilities that produce the mineral slurries, and from these slurries the excess water must be removed to acquire the valuable minerals. The dewatering process endeavors to achieve liquid water removal from the concentrated mineral slurry. A goal of the dewatering process is to decrease the residual liquid water content of the starting mineral slurry concentrate. Dewatering additives such as flocculants in combination with an anionic surfactant have been added to concentrated mineral slurries to reduce the liquid water content of the treated slurry being subjected to filtration. In theory, dewatering aids should increase production rates as well as decrease the amount of water present in the filtered ore or mineral cake solids. Because the filtered solids contain less water, the overall production is expected to increase. However, in practice this is not always observed because it produces further requirements of production facility requirements. Traditionally, polymers have been used to agglomerate solids and increase the filtration rate. However, polymers substantially increase the costs. In many instances, the end use or processing of the mineral is detrimentally affected by the higher cost.
There is a need to decrease the cost of the production of minerals, rather than a volume of product. Elimination of the moisture in the filter cake or centrifuge solids increases the amount of mineral or ore solids on a weight percent basis, thereby reducing freight costs required for transport or energy costs for further drying or processing per kilogram of the mineral, or ore solids.
Thus, it is known by those skilled in the art that generally when the moisture content of an aqueous mineral slurry concentrate is beneficially reduced by use of certain additives, a disadvantage also occurs in that the production of the resulting filter cake is decreased at the expense of achieving the beneficial dewatering. None of the background art processes have addressed both the need to reduce the residual liquid water content of the concentrated mineral slurry while simultaneously increasing the production of the mineral concentrate filter cake that results from the water removal process such as for example but not limited to a filtration process.
U.S. Pat. No. 4,207,186 (Wang '186) provides a process for dewatering mineral and coal concentrates comprising mixing an aqueous slurry of a mineral concentrate and an effective amount of a dewatering aid that is a combination of hydrophobic alcohol having an aliphatic radical of eight to eighteen carbon atoms and a nonionic surfactant of the formula R—(OCH.sub.2CH.sub.2).sub.xOH wherein x is an integer of 1-15, R is a branched or linear aliphatic radical containing six to twenty-four carbon atoms in the alkyl moiety, and subjecting the treated slurry to filtration. Wang et al. '186 states that when a hydrophobic alcohol such as decyl alcohol is combined with a nonionic surfactant, lower moisture contents are obtained with iron ore concentrate than had a dewatering aid not been employed. Wang et al. '186, however, is unconcerned with increasing the production of the resulting filter cake.
U.S. Pat. No. 4,210,531 (Wang '531) provides a process for dewatering mineral concentrates which consists essentially of first mixing with an aqueous slurry of a mineral concentrate an effective amount of a polyacrylamide flocculant, and next mixing with the flocculant-treated slurry an effective amount of a combination of an anionic surface active agent composition and a water insoluble organic liquid selected from aliphatic hydrocarbons, aromatic hydrocarbons, aliphatic alcohols, aromatic alcohols, aliphatic halides, aromatic halides, vegetable oils and animal oils, wherein the water-insoluble organic liquid being different from any water-insoluble organic liquid present in the anionic surface active agent composition, and thereafter removing the water as a liquid from the slurry. Wang et al. '531, however, does not address and is unconcerned with reducing the residual liquid water content of the concentrated mineral slurry and increasing the production of the resulting filter cake, nor does it address the expanded costs because of added production requirements.
Additionally, there are fundamental differences in the drying of techniques Wang '186 and Wang '531 because these techniques relate to the drying of coal. The coal drying techniques are different because of the mineral elements of the mineral slurry, as well the origination of the drying process being applied to the mineral slurry concentrate versus coal.
Concurrently, there are known technologies called molecular sieves, including the co-pending patent application Ser. No. 12/924,570 providing for the application of molecular sieves to coal fines. Similar to the shortcomings of Wang '186 and Wang '531 to coal, similar differences exist between the application of molecular sieves to coal fines versus mineral slurry concentrate having mineral slurry contained therein. In addition to the higher starting moisture content of the mineral slurry compared with coal fines, there is also a different moisture distribution between surface moisture and inherent moisture. There are also differences in physical properties of the material science of mineral slurry compared with coal fines, including differences for the processing of the dewatering techniques as described in further detail below. Moreover, there are cost limitations with molecular sieves.
Relative to mining, existing mineral slurry dewatering techniques have limited benefits with large environmental concerns. As such, there exists an economical need for a method and system for drying mineral slurries to reduce the moisture content, thereby improving the harvest of minerals and reducing environmental impact.
Technologies have been explored for drying that involve adsorption of water using desiccants and zeolites. These technologies have only been employed where the use of high temperatures degrade the materials which are sought to be dried, such as foodstuffs and materials that are known to chemically react and/or degrade with heat from the thermal drying process thereby making conventional thermal drying techniques infeasible. For example, U.S. Pat. No. 3,623,233, entitled “Method of Drying a Damp Pulverant,” filed Dec. 3, 1969 to Severinghaus describes heat drying of calcite (CaCO3). Severinghaus teaches that heat drying of calcite results in calcination and production of calcine (CaO), which is detrimental to the use of calcite in fillers and extenders. Similarly, U.S. Pat. No. 6,986,213, entitled “Method for Drying Finely Divided Substances,” filed Jul. 3, 2003 to Kruithof describes drying foodstuffs such as wheat flour which are degraded using thermal drying techniques. The use of such techniques for drying materials such as mineral slurries that can be dried without degradation using conventional techniques has not been explored.
A longstanding need exists for an economical method and system for drying mineral slurries to reduce the moisture content and to prevent the substantial loss of mineral content in the drying process. Any reduction in moisture thereby increases the cost-effectiveness of mineral slurry processing.